Removing beams from the ceiling?

Hello, I live in a townhouse with four floors and on the side of the townhouse which is exposed, I have a leak in the ceiling on the ground floor whenever there is a wind driven rain. Water drips out from one particular area in the ceiling, and there is also a drip in the heat vent on the lower part of the same wall. At first, I thought it was due to a lack of caulking in my deck, which is on the second floor, but I did a lot of caulking on the deck, and it's still happening. I called a roofing company and I am waiting for them to send someone. They said they think it is definitely a problem with the roof, especially since I am missing an aluminum siding. But if it was an issue with the roof, why would there be no leak on the 4th, 3rd, or 2nd floor, and only on the ground floor. Does anybody know what could be the cause of this leak, or how it could be diagnosed? Thank You.

When I originally installed my outlet box for my ceiling fan I didn't really do a good job. It's not level and when I tightened it , it took out some of the drywall. It's not a huge hole just kinda crumbled around the edges. We are fixing to redo our entire den and I want to redo it and hang the box level this time. So I guess my question is this..if I cut out just a say 1' x my joist spacing and screw a new piece in do I really have to tape and mud that. I was just going to mud it, patch the popcorn and prime and paint. Any help is appreciated.